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6 - Sixth Eastern Wildlife Damage Control Conference (1993) Eastern Wildlife Damage Control Conferences

October 1993

USE PATTERNS OF NUISANCE BLACK-CROWNED NIGHT HERONS ON A HYDROELECTRIC IN EASTERN TENNESSEE

Michael A. Wefer University of Tennessee

Joseph W. Lee University of Tennessee

William G. Minser University of Tennessee

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Wefer, Michael A.; Lee, Joseph W.; and Minser, William G., "USE PATTERNS OF NUISANCE BLACK- CROWNED NIGHT HERONS ON A HYDROELECTRIC DAM IN EASTERN TENNESSEE" (1993). 6 - Sixth Eastern Wildlife Damage Control Conference (1993). 36. https://digitalcommons.unl.edu/ewdcc6/36

This Article is brought to you for free and open access by the Eastern Wildlife Damage Control Conferences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in 6 - Sixth Eastern Wildlife Damage Control Conference (1993) by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. USE PATTERNS OF NUISANCE BLACK-CROWNED NIGHT HERONS ON A HYDROELECTRIC DAM IN EASTERN TENNESSEE

MICHAEL A. WEFER, Department of Forestry Wildlife and Fisheries, University of Tennessee, Knoxville TN 37901

JOSEPH W. LEE, Department of Forestry Wildlife and Fisheries, University of Tennessee, Knoxville TN 37901

WILLIAM G. MINSER, Department of Forestry Wildlife and Fisheries, University of Tennessee, Knoxville TN 37901

ABSTRACT: Black-crowned night heron (Nycticorax nycticorax) droppings are a problem on Hydroelectric Dam. Annual and daily use patterns were monitored to determine when and what areas of the dam the herons were using. The dam was used primarily during the breeding season (April-July) and received 24.2% more use in the evenings than in the morning. The most use occurred in June with a high of 211 birds 12 June 1991 and 266 birds 5 June 1992. Herons used band railings on the dam the most (66%) for perching. About 12% of the night herons using the dam were juveniles. Because most of the use occurred in April through June, we suggest that damage control efforts be concentrated at this time and we suggest methods of control.

Proc. East. Wildl. Damage Control Conf. 6:182-184. 1995.

Wading bird predation at fish rearing facilities is a entire width of the darn and to use netting and monofilament common problem faced by wildlife managers (Mort 1978, or wire exclusion to force herons off the railings and onto the Hoy et al. 1989), however, wading birds can also create alternate perch. Before further control methods were sanitation problems or cause property damage. Black-crowned undertaken, a more thorough assessment of the night heron night heron droppings have become a problem at the Fort use of dam facility was initiated. Loudoun Hydroelectric Plant operated by the Tennessee Valley Authority (TVA) located in Lenoir City in Loudon County, We thank K.M. Blanton for providing technical support Tennessee. The plant is part of Fort Loudoun Dam which for this research and for reviewing this manuscript and impounds the to form . providing helpful comments. The herons feed in the tailwaters below the dam where they find an abundant supply of shad (Dorsoma spp.) and have METHODS established a rookery about 1 km from the dam. The railings on the facility are used by the herons as perches when they Night heron use of Fort Loudoun dam tailwaters were are not feeding and their droppings collect on the railings, the monitored twice weekly beginning 29 April 1991 and ending sidewalk and the face of the dam. The droppings corrode the 22 April 1992. Ancock and Kushlan (1984) reported that railings, produce a foul odor, and represent a potential health black-crowned night herons feed most crepuscularly and at risk to people. There is also the potential of the night herons night. Because accurate counts could not be made at night, 1 colliding with and damaging electrical equipment at the facility 15 minute count was made at sunrise once per week and 1 15 (Enck 1989). minute count was made 1 hour before sunset once per week. Specific location and age of herons using the dam was United States Department of Agriculture, APHIS, Animal recorded. Damage Control (ADC) personnel began efforts to reduce night heron damage in 1990 with the use of pyrotechnics, Because greatest heron use was found to occur at sunset recorded distress calls, and other harassment measures, but the morning counts were discontinued. One 15 minute count were unsuccessful (K.M. Blanton, pers. commun.). An was made 1 hour before sunset per week May - August 1992. experimental trapping and translocation program was Herons were similarly monitored in 1993 from 22 July through attempted in 1991, but the herons responded poorly to the 22 August. bait of live shad and only 8 were trapped and translocated. In late winter of 1992 ADC and TVA discussed the use of The number of herons nesting and produced in the rookery alternate perches and exclusion techniques to reduce the heron was estimated during the 1991 and 1992 nesting season (May damage (K.M. Blanton, pers. commun.). In February TVA June). In 1993 the rookery was checked in August to determine installed a 15 m section of pipe on the railings of the lower if it was still active. Only 1-4 visits per nesting season were deck of the powerhouse, which extended a few meters out made to the rookery to limit any adverse effects the visits over the water. After the night herons were seen using the might have on renesting attempts (Tremblay and Ellison 1979). pipe as a perch, plans were made to extend the pipe across the RESULTS to 12.8 in 1992. In 1991 11.9% of the total night herons using the dam were juveniles and 12.0% were juveniles in 1992. Night herons used the dam most in June in 1991 and 1992 Night herons perched on the dam’s railings comprised 65.9% with extensive use made April through July (Fig. 1.). The of the birds observed and 20.8% used rocks below the dam average number of night herons using Fort Loudoun Dam 1 while feeding on shad. hour before sunset from May 1991 to April 1992 was 55.8, 24.2% higher than the average of 42.3 counted at sunrise. The nightly average of night herons observed 22 July 1993 The annual average number of adults using the dam May 1991 through 22 August 1993 was 42.8. This is a 6.5% decrease through April 1992 was 45.7 (82.0%) compared to the average from an nightly average of 45.8 during the same period in of 10.1 (18.0%) juveniles using the dam. The maximum 1992. During this period 12.9% of the birds observed were number of herons counted during one observation was 211 on juveniles. 12 June 1991 and 266 on 5 June 1992. The dam received low use during the winter months (Fig. 1.) as night herons are Approximately 200 nestlings were counted in the night migratory. The birds using the dam in the winter may be heron rookery during both the 1991 and 1992 nesting season. migrants from farther north (Hancock and Kushlan 1984). The Many of the trees in the rookery had fallen in 1993 as a result nightly average May through August 1992 was 107.3 herons, of a spring blizzard and the rookery bad been abandoned. It a 9% increase over an average of 97.8 for the same period in appeared that at least part of the population had relocated to 1991. The nightly average number of juveniles using the dam nest in a great blue heron (Ardea herodias) rookery area during this period increased slightly from 11.8 in 1991 approximately 9.6 km downstream from the dam.

Fig. 1. Monthly averages of evening counts of black-crowned night herons using Fort Loudoun Hydroelectric Facility, Loudon County, Tennessee, May 1991 - August 1992. DISCUSSION LITERATURE CITED

The concentration of shad below Fort Loudoun Dam Enck, J. W. 1989. Wildlife damage in electrical substations in provides an abundant food source for the night herons and is New York. Proc. Eastern Wildl. Damage Control Conf. likely the reason the birds established a rookery nearby and 4:225-231. concentrate around the dam. Instead of trying to drive the herons away which would be difficult as long as the food Ancock, J. and J. Kushlan. 1984. The herons handbook. Harper source exists, we recommend habitat modification to reduce & Row, New York. p188-192. the damage problems. Construction of alternate perches and use of exclusion devices may help reduce the herons use of Hoy, M.A., J.W. Jones, and A. Bivings. 1989. Economic the railings as perches. Periodic washing of the decks and Impact and control of wading birds at Arkansas. Proc. rails with a powerwasher as needed would reduce much of Eastern Wildl. Damage Control Conf. 4:109-112. the odor and corrosion problems associated with the heron droppings. Mort, D.F. 1978. Control of wading bird predation at fish- rearing facilities. Research Rpt. #7, Nat. Audubon Soc. The abandonment of the original rookery upstream from p. 131-132. the dam and establishment of new rookery further downstream may effect night heron use patterns in the dam area. The slight Tremblay, J. and L.N. Ellison. 1979. Effects of human drop in use July - August 1993 may indicate a change in use disturbance on breeding of Black-crowned Night Herons. patterns. The use of the dam area should be monitored in 1994 Auk 96:364-369. to measure changes in use and to measure effectiveness of the alternate perches that are to be constructed by TVA in 1994. A decision on remedial action could be made after the 1994 assessment.